Cooking system comprising a directly heated glass-ceramic plate

Abstract

A cooking system based on the principle of heat conduction and having a one-piece cooking surface made of a glass-ceramic material. The cooking surface has a cooking area which can be directly heated in an individual manner by heating elements placed on the underside of the glass-ceramic plate. The glass-ceramic plate has main crystal phases, high quartz mixed crystal or keatite mixed crystal, primarily formed from constituents LiO 2 —Al 2 O 3 —SiO2, with a coefficient of expansion of α=0 to 1.5×10 −6 /K, preferably α=0 to 1×10 −6 /K, and with a thermal conductivity of <3 W/mK, preferably of <2.7 W/m K. The glass-ceramic plate also has at least one cooking area situated on an underside of the plate. In addition, the heating elements of the cooking areas are of metallic layers, and a porous ceramic layer is placed between the underside of the glass-ceramic plate and the heating elements while serving as an electrical insulation layer. The optical appearance and the cleanability of the cooking system are thus improved, and it is possible to directly apply a durable heating layer system while considerably increasing the cooking capacities.

1 . A cooking system using heat conduction and having a one-piece cooking surface made of a glass-ceramic material and having at least one cooking zone which can be individually directly heated by heating elements arranged on an underside of a glass-ceramic plate, the cooking system comprising: 
 the glass-ceramic plate having main crystalline phases of one of high quartz mixed crystal and keatite mixed crystal type mainly formed of components LiO 2 —Al 2 O 3 —SiO 2  with a coefficient of expansion of α=0 to 1.8×10 −6 /K and a heat conductivity of <3 w/mK, and having at least one cooking zone on the underside,    the heating elements ( 30 ) of the cooking zone having metallic layers, and    between the underside ( 11 ) of the glass-ceramic plate ( 10 ) a porous ceramic layer arranged as an electrical insulating layer ( 20 ).    
     
     
         2 . The cooking system in accordance with  claim 1 , wherein the coefficient of expansion α=0 to 1.5  10   −6 /K.  
     
     
         3 . The cooking system in accordance with  claim 2 , wherein the heat conductivity has a value <2.7 W/mK.  
     
     
         4 . The cooking system in accordance with  claim 2 , wherein during a cooking operation at 550° C. the cooking zone shows arching in a diagonal direction <0.2 mm.  
     
     
         5 . The cooking system in accordance with  claim 4 , wherein the heating elements ( 30 ) are applied by thermal spray methods, including one of atmospheric plasma spray methods and cold gas spray methods of one of NiCr base alloys, NiAl base alloys, CrFeAl base alloys and oxidation-resistant cermets, including Cr 3 C 2 —NiCr or WC—CoCr.  
     
     
         6 . The cooking system in accordance with  claim 4 , wherein the heating elements ( 30 ) are applied by screen printing methods from Ag/Pd-containing pastes with a glass frit.  
     
     
         7 . The cooking system in accordance with  claim 6 , wherein the ceramic layer used as an insulating layer ( 20 ) is of one of Al 2 O 3 , mullite, cordierite, circonium silicate and SiO 2 /TiO 2 .  
     
     
         8 . The cooking system in accordance with  claim 7 , wherein the insulating layer ( 20 ) is bonded to the underside ( 11 ) of the glass-ceramic plate ( 10 ) by thin strips ( 21 ) of primary ceramic particles of a width of approximately 50 to 150 nm.  
     
     
         9 . The cooking system in accordance with  claim 8 , wherein the heating elements ( 30 ) are covered by a thermal insulating layer ( 40 ) of silicate fiber materials.  
     
     
         10 . The cooking system in accordance with  claim 9 , wherein the glass-ceramic plate ( 10 ) has a specific resistance >10 5  Ω, and the cooking system has a breakdown resistance of >3750 V, and a leakage current is <0.25 mA per cooking zone.  
     
     
         11 . The cooking system in accordance with  claim 1 , wherein the heat conductivity has a value <2.7 W/mK.  
     
     
         12 . The cooking system in accordance with  claim 1 , wherein during a cooking operation at 550° C. the cooking zone shows arching in a diagonal direction <0.2 mm.  
     
     
         13 . The cooking system in accordance with  claim 1 , wherein the heating elements ( 30 ) are applied by thermal spray methods, including one of atmospheric plasma spray methods and cold gas spray methods of one of NiCr base alloys, NiAl base alloys, CrFeAl base alloys and oxidation-resistant cermets, including Cr 3 C 2 —NiCr or WC—CoCr.  
     
     
         14 . The cooking system in accordance with  claim 1 , wherein the heating elements ( 30 ) are applied by screen printing methods from Ag/Pd-containing pastes with a glass frit.  
     
     
         15 . The cooking system in accordance with  claim 1 , wherein the ceramic layer used as an insulating layer ( 20 ) is of one of Al 2 O 3 , mullite, cordierite, circonium silicate and SiO 2 /TiO 2 .  
     
     
         16 . The cooking system in accordance with  claim 1 , wherein the insulating layer ( 20 ) is bonded to the underside ( 11 ) of the glass-ceramic plate ( 10 ) by thin strips ( 21 ) of primary ceramic particles of a width of approximately 50 to 150 nm.  
     
     
         17 . The cooking system in accordance with  claim 1 , wherein the heating elements ( 30 ) are covered by a thermal insulating layer ( 40 ) of silicate fiber materials.  
     
     
         18 . The cooking system in accordance with  claim 1 , wherein the glass-ceramic plate ( 10 ) has a specific resistance >10 5  Ω, and the cooking system has a breakdown resistance of >3750 V, and a leakage current is <0.25 mA per cooking zone.